There are a wide number of acoustical transducers which provide for the conversion of energy between electrical and mechanical stimuli and which include the employment of a piezoelectric element to operate in a planar mode, particularly to provide for the conversion of electric energy to acoustical energy over a wide range of frequencies, such as in a high-frequency speaker. One such high-frequency transducer is described in U.S. Pat. No. 3,548,116, wherein a piezoelectric annular wafer is adhesively and directly mounted at the apex of a compliant diaphragm, with the diaphragm providing the sole support for the piezoelectric element, whereby the mass of the piezoelectric wafer assembly provides inertia for the operation of the transducer.
In another high-frequency, acoustical transducer, such as that described in U.S. Pat. No. 3,786,202, the transducer comprises a piezoelectric element secured to a truncated apex area of a diaphragm, the area defining a circular area, the diameter of which is less than the diameter of the first overtone node of the piezoelectric wafer, and wherein the piezoelectric wafer is directly secured within the circular area of the resilient diaphragm. In addition, a rubber damping disc is affixed at the opposite surface of the piezoelectric wafer, to lower the fundamental resonance frequency and to damp the peak output of the fundamental and first overtone resonance frequencies, thereby providing a flat frequency response over a desired band width.
It is desirable to provide a narrow-frequency band, acoustical transducer having a high conversion efficiency over the narrow band of frequency; for example, for use as a sound-emitting beeper device.